Conventionally, a data communication system for mobile communication, referred to as a multimedia mobile access system (MMAC), has been proposed. This access system is a high-speed radio access system which is seamlessly connectable to an optical fiber network (BISDN). In this access system, a relatively high frequency band of 5 GHz or the like and a transmission rate of approximately 30 Mbps are used, and a TDMA (time division multiple access)/TDD (time division duplex) mode is used as an access mode.
Meanwhile, in allocating transmission data to a plurality of subcarriers for carrying out radio transmission by applying the multi-carrier signal transmission mode referred to as an orthogonal frequency division multiplex (OFDM) mode as in the MMAC system, there is a problem that a large peak power ratio of the transmission power to the average power is generated. For example, if the number of subcarriers is 32, the ratio is simply equal to 10 log 32=15 dB. Therefore, in the case where the multi-carrier signal transmission mode is employed, it is necessary to use a power amplifier having broad linearity as a power amplifier of a transmission section of a transmission device. Thus, in a small-size terminal unit which has low power efficiency and is required to have low dissipation power for battery driving, there is an extremely large burden on the unit.